Many copper and gold containing ores and concentrates contain silver to such a degree that is it economically reasonable to recover it. However, an efficient recovery of silver is rather difficult from a chloride-bromide based leaching solution. Silver concentration of the leach solution is usually low compared to copper and calcium and/or sodium concentrations. Furthermore, concentration of many leached metals like iron, zinc and lead can also be higher that the silver concentration. There are some process options for silver recovery such as cementation, sulfide precipitation or solvent extraction. Some of these processes are not suitable for chloride-bromide based leaching solutions where especially copper is present in very high concentrations.
US 20100116093 Al discloses a method of recovering silver from a hydrochloric acid solution containing alkali and/or alkali earth metal chloride, silver, copper and iron ions, comprising the steps of: (1) bringing the solution into contact with a strong-base anion-exchange resin (such as PA-312 made by Mitsubishi Chemical Corporation) to adsorb silver, copper, and iron in the anion-exchange resin; (2) washing the anion-exchange resin with water to remove the adsorbed copper and iron; and (3) then bringing the ion-exchange resin into contact with a hydrochloric acid solution to elute the adsorbed silver.
One of the disadvantages associated with the above arrangement is that most of the copper must be removed prior to contact with anion-exchange resin by solvent extraction to achieve a copper concentration of from about 20 g/L to about 30 g/L. Furthermore, according to the publication the upper limit of the concentration of silver in the acidic solution is desirably 30 mg/L due to absorption limit of strong-base anion exchange resin.